Scoop: 20/20 on ABC - Friday, September 8, 2017

Self-defense or murder? That is the question dividing Flagstaff, Arizona, following a shooting on the campus of Northern Arizona University a few weeks into the 2015 fall semester.

Friday night "20/20" reports on the tragedy and the trial's surprising conclusion. It was a typical Thursday night, with a party at "The Courtyard" - where some NAU students live - around 1:00 a.m. witnesses heard a verbal altercation outside the party and then gunshots. When police reached the scene, they found junior Colin Brough dead, his fraternity brothers Nick Piring, Kyle Zientek and Nick Prato wounded and freshman Steven Jones identifying himself as the gunman. Steven claimed that he shot them out of self-defense. Prosecutors disagree and charge him with first-degree murder.

According to Steven, he and his friends were walking back to campus and looking for a friend when several guys from inside the party came out and started harassing them. Steven says that out of nowhere someone ran up behind him and sucker punched him in the face. Terrified, Steven ran to his car believing he was being chased by some of the guys from the party. In his car and panicking he could not find his keys so he did the only thing he says he thought to do - reach into his glove box and pulled out his gun. Steven claims he yelled to the guys he believed were pursuing him, warning them that he had a gun, and that they said they were going to kill him so he fired two shots at each of the boys in front of him. Then he says he was taken to the ground by a group of guys and fired several more times into the air to disperse the crowd, hitting two more students. The prosecution believes that Steven was not in fear for his life when he fired his gun, and the case goes to court. After five days of deliberations the jury comes back with a surprising conclusion that shocks the court.

"20/20" is anchored by Elizabeth Vargas and David Muir. David Sloan is senior executive producer.